Use of the Malthus Microbial Growth Analyser to study the post antibiotic effect of antibiotics

The post antibiotic effect (PAE) of ceftazidime, ciprofloxacin, mecillinam and imipenem alone and in combination against Gram-negative bacteria was assessed by a new technique using a Malthus Microbial Growth Analyser. Ciprofloxacin gave the most prolonged and consistent PAE (1.3-2.9 h) and imipenem also gave a significant PAE against some bacterial strains (up to 1.3 h). The PAE of both antibiotics was dependent on concentration. The PAE of combinations of ciprofloxacin and imipenem often showed less PAE than was present with either agent alone. Ceftazidime gave no significant PAE (-1.5-0.4 h), though mecillinam consistently gave a short PAE (approximately 0.5 h) against Escherichia coli. The new method allows for the rapid and labour saving evaluation of PAE. We believe that further studies on PAE of antibiotic combinations are desirable.